Obstructive Sleep Apnea Hypopnea Syndrome (OSAHS) is a highly prevalent disease where snoring is one of the most common symptoms. OSAHS occurs during sleep due to collapsing of upper airways leading to cessation of breathing. The narrowing of airways and the relaxed muscles surrounding the airways generally results in snoring. OSAHS is a classic example for a treatable disease, which, by it self is not life-threatening. However, if left untreated, it causes an avalanche of devastating complications such as reduction in cognitive function, cardiovascular diseases, decreased quality of life, fatigue and increased vulnerability to accidents [1].
Full closure of the airways is known as obstructive sleep apnea and a partial closure is defined as obstructive hypopnea. OSAHS severity is expressed by the Apnea-Hypopnea-Index (AHI), which computes the number of Apnea and Hypopnea events per hour, averaged over the total sleep time. The following conventions are currently in clinical use: AHI<5 (no OSAHS), 5<AHI<15 (mild OSAHS), 15<AHI<30 (moderate OSAHS) and AHI>30 (severe OSAHS). Some researchers also use AHI=10 as the threshold for diagnosing the disease.
The current accepted diagnosis for OSAHS is by supervised overnight Polysomnography (PSG) to record a multitude of physiological signals for manual analysis at a sleep laboratory. Thus it is very expensive and time consuming. Limited PSG facilities around the world have resulted in long waiting lists and over 80%-90% individuals with OSAHS currently remain undiagnosed in Australia [2].
There has been a flurry of recent activities at developing technology to address this need [3 and references therein] for simplified diagnostic methods. The main focus of these activities was the development of ambulatory sleep instrumentation hardware.
The National Sleep Disorders Research Plan [4], USA, 2003, reports that the single-signal and full PSG systems meant for home monitoring yielded mixed results, and that none was sufficiently effective for routine use. One of the main problems faced by such devices is that the service of an experienced medical technologist is still required at the site of the test, if acceptable sensitivity/specificity performance is required.
It is an object of the invention to provide a method and apparatus for diagnosing a sleeping disorder in a subject that is an improvement, or at least a useful alternative, to the previously surveyed approaches of the prior art.